you need a AS file with the name “ImageMovie.as” with this code in there
[as]
// #3
package {

import flash.display.MovieClip;

public class ImageMovie extends MovieClip {

function ImageMovie(xPos:Number = 0,yPos:Number = 0) {
this.x = xPos;
this.y = yPos;
}
}
}
[/as]
and you need this code in the timeline, because the movieClip in the Library is linked to this AS file you can talk to it directly:
[as]
/*
How to “attachMovie” in as3
*/
var imageMC:ImageMovie = new ImageMovie(50,50);
this.addChild(imageMC);
[/as]
and the it will work the same as option 3 in AS2